Hydrogarnet process as a modern approach to hydrometallurgical alkaline processing of low-grade bauxites. Review

In current conditions, energy costs are becoming the decisive factor threatening the existence of alumina industry. Hydrochemical processes are relevant for low-grade bauxites and red muds as, due to high availability of such materials (as compared with the high-grade ones), a critical rise of energy costs (gas, fuel oil, coal) can be offset when relying on the conventional Bayer process. This paper considers the results of studies aimed at the development and implementation of Bayer-hydrogarnet process to be applied to low-grade bauxites and dumped red muds. The sodium and aluminium oxides contained in red mud get regenerated in the hydrogarnet cycle and get returned to the Bayer process, while the new solid product synthesized, which carries all the bauxite iron, silicon, calcium and trace elements, is converted into various commodities. The authors demonstrate that, irrespective of the origin of bauxites and red muds, this technology enables to achieve high recovery of valuable components into final products while minimizing pollution. Recent developments concerning the equipment used and the actual process were aimed at streamlining the process, raising the recovery of aluminium oxide and expanding the range of by-products. Apart from producing alumina and aluminium hydroxide, the low-waste hydrogarnet process can be used to produce cast iron, pigments, ameliorants, building materials and others. Tests conducted at different scales prove that the process can be applied to different grades of bauxite.